Carb Adjustment


New Member
Mar 30, 2015
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Ilmenau / Thuringia/ Germany
Hello Friends!

I would be pleased if you could help me to adjust my carburetor of my stock 69 non HP 440 in my 70 Polara Coupe.
I installed a 735 Quick Fuel SS carburetor with 65 primary jets, 7,5 power valve, 28 IFRs, 70 Idle Air bleeds and dark green cam.

I have done a test drive with wideband lambda and some problems with a to lean or fat mixture.

An idle adjustment of mixture is no problem with mixture screws, i have 16 inhg vacuum.
When i accelerate, at first mixture goes much to lean then at once its going to fat.

Please see in my Video.

Does anybody maybe have an idea or a tip for a proper standard configuration for this motor?

Because in this case i think im running in idle circuit but this are big differences...

Thank you all very much in advance!
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Use a vacuum gauge. The highest it goes is where you want it from manifold vacuum.
Pretty good article on adjusting out wide open throttle bogging in this month’s Mopar Action. Talks about Holley Carter etc etc...
(Wondering "why" a QuickFuel carb on a stock motor?)

Adjust the idle mixture first, either to highest manifold vacuum at the factory-spec idle rpm or by the lean-best-idle method.

The accel pump is supposed to help get past the transition between the idle system and the starting of the main system fuel, on acceleration. In normal "easy" driving, the transition ports near the idle needle discharge ports do this. The factory power valve on Holleys, back then, was usually 5.5" Hg, so the one you have will come in sooner, fwiw.

As far as the AFR checks go, make sure the engine AND lambdy sensor are fully up to operating temp for accurate checks. First aim for about 14.2 at hot base idle (at factory spec idle rom). Second, at about 2000rpm cruise, with non-ethanol'd fuel, aim for about 14.7 (which relates to the main jet sizing AND the various air bleeds sizing in the main system).

How do the spark plugs look, ceramic coloration and such?

Just some thoughts,
Powervalve number half of what idle vacuum is. Your 7.5 should be okay. I'm trying to remember, that lean/rich has so.ething to do with the power valve orfice size and the accel pump. What I would do if its driveable... cruise at 2000rpm and see what the number is there. You want to get this close to lambda 1 by changing main jets. The idle mixture id be aiming for a 0.95 probably. Once this is dialed in I would fully concentrate on the accel circuit with the squirter and power valve. You need a vacuum gauge to check the power valve. Do your cruise speed and find an uphill street. Slowly accelerate uphill and watch the vacuum go to wherever your Powervalve is rated, then look at the lambda.

Actually watching the video, does it go to Lambda .7 when you let off the gas???
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Sorry for my late reply, due to normal work, i can work on my car only irregular.
I think im currently on a good way.
With 67 primary jets, cruise above 50 Miles are okay and i changed idle air bleeds from 70 to 65 and idle feed restrictors from 30 to 34 and Power valve to 9.5.
Now cruise till 50 miles is also okay, the car runs currently very well!
Only when i push throttle pedal very soft, the car goes sometimes to lambda 1.06... But only if i push very very soft, so maybe its normal? 1 Millimeter more and lambda goes down to 0,90-0,95. (10-30 miles)
A carburetor has three different fuel supplies. Idle, transfer and main circuit. It will go lean on a transition between any of these. If you the accelerator pump covers this just not very precise. If drivability is good and not black smoke chugging out when you gas on it your probably close enough. Best just to target air fuel at idle, cruise, and WOT. Then go back and try to cover drivability issues; stumble, big, sputter, and chugging black smoke.
#65 is really lean on primary side for cruise IMO
Only when i push throttle pedal very soft, the car goes sometimes to lambda 1.06... But only if i push very very soft, so maybe its normal? 1 Millimeter more and lambda goes down to 0,90-0,95. (10-30 miles)

This is normal and you are reaching your PV value right when you see the lambda drop. 1.06 I wouldn't worry too much. It sounds like you are on a good path. Now you can check your hard acceleration numbers and dial in the squirter and pump!